391 lines
9.4 KiB
Go
391 lines
9.4 KiB
Go
// Copyright 2020 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package buffer
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import (
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"fmt"
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"io"
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)
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// View is a non-linear buffer.
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//
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// All methods are thread compatible.
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//
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// +stateify savable
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type View struct {
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data bufferList
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size int64
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}
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// TrimFront removes the first count bytes from the buffer.
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func (v *View) TrimFront(count int64) {
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if count >= v.size {
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v.advanceRead(v.size)
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} else {
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v.advanceRead(count)
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}
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}
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// ReadAt implements io.ReaderAt.ReadAt.
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func (v *View) ReadAt(p []byte, offset int64) (int, error) {
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var (
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skipped int64
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done int64
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)
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for buf := v.data.Front(); buf != nil && done < int64(len(p)); buf = buf.Next() {
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needToSkip := int(offset - skipped)
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if sz := buf.ReadSize(); sz <= needToSkip {
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skipped += int64(sz)
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continue
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}
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// Actually read data.
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n := copy(p[done:], buf.ReadSlice()[needToSkip:])
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skipped += int64(needToSkip)
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done += int64(n)
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}
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if int(done) < len(p) || offset+done == v.size {
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return int(done), io.EOF
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}
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return int(done), nil
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}
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// advanceRead advances the view's read index.
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//
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// Precondition: there must be sufficient bytes in the buffer.
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func (v *View) advanceRead(count int64) {
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for buf := v.data.Front(); buf != nil && count > 0; {
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sz := int64(buf.ReadSize())
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if sz > count {
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// There is still data for reading.
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buf.ReadMove(int(count))
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v.size -= count
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count = 0
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break
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}
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// Consume the whole buffer.
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oldBuf := buf
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buf = buf.Next() // Iterate.
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v.data.Remove(oldBuf)
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oldBuf.Reset()
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bufferPool.Put(oldBuf)
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// Update counts.
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count -= sz
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v.size -= sz
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}
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if count > 0 {
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panic(fmt.Sprintf("advanceRead still has %d bytes remaining", count))
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}
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}
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// Truncate truncates the view to the given bytes.
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//
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// This will not grow the view, only shrink it. If a length is passed that is
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// greater than the current size of the view, then nothing will happen.
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//
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// Precondition: length must be >= 0.
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func (v *View) Truncate(length int64) {
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if length < 0 {
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panic("negative length provided")
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}
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if length >= v.size {
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return // Nothing to do.
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}
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for buf := v.data.Back(); buf != nil && v.size > length; buf = v.data.Back() {
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sz := int64(buf.ReadSize())
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if after := v.size - sz; after < length {
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// Truncate the buffer locally.
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left := (length - after)
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buf.write = buf.read + int(left)
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v.size = length
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break
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}
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// Drop the buffer completely; see above.
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v.data.Remove(buf)
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buf.Reset()
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bufferPool.Put(buf)
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v.size -= sz
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}
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}
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// Grow grows the given view to the number of bytes, which will be appended. If
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// zero is true, all these bytes will be zero. If zero is false, then this is
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// the caller's responsibility.
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//
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// Precondition: length must be >= 0.
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func (v *View) Grow(length int64, zero bool) {
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if length < 0 {
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panic("negative length provided")
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}
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for v.size < length {
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buf := v.data.Back()
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// Is there some space in the last buffer?
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if buf == nil || buf.Full() {
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buf = bufferPool.Get().(*buffer)
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v.data.PushBack(buf)
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}
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// Write up to length bytes.
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sz := buf.WriteSize()
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if int64(sz) > length-v.size {
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sz = int(length - v.size)
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}
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// Zero the written section; note that this pattern is
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// specifically recognized and optimized by the compiler.
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if zero {
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for i := buf.write; i < buf.write+sz; i++ {
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buf.data[i] = 0
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}
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}
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// Advance the index.
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buf.WriteMove(sz)
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v.size += int64(sz)
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}
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}
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// Prepend prepends the given data.
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func (v *View) Prepend(data []byte) {
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// Is there any space in the first buffer?
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if buf := v.data.Front(); buf != nil && buf.read > 0 {
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// Fill up before the first write.
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avail := buf.read
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bStart := 0
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dStart := len(data) - avail
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if avail > len(data) {
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bStart = avail - len(data)
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dStart = 0
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}
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n := copy(buf.data[bStart:], data[dStart:])
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data = data[:dStart]
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v.size += int64(n)
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buf.read -= n
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}
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for len(data) > 0 {
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// Do we need an empty buffer?
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buf := bufferPool.Get().(*buffer)
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v.data.PushFront(buf)
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// The buffer is empty; copy last chunk.
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avail := len(buf.data)
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bStart := 0
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dStart := len(data) - avail
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if avail > len(data) {
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bStart = avail - len(data)
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dStart = 0
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}
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// We have to put the data at the end of the current
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// buffer in order to ensure that the next prepend will
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// correctly fill up the beginning of this buffer.
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n := copy(buf.data[bStart:], data[dStart:])
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data = data[:dStart]
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v.size += int64(n)
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buf.read = len(buf.data) - n
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buf.write = len(buf.data)
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}
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}
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// Append appends the given data.
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func (v *View) Append(data []byte) {
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for done := 0; done < len(data); {
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buf := v.data.Back()
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// Ensure there's a buffer with space.
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if buf == nil || buf.Full() {
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buf = bufferPool.Get().(*buffer)
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v.data.PushBack(buf)
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}
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// Copy in to the given buffer.
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n := copy(buf.WriteSlice(), data[done:])
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done += n
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buf.WriteMove(n)
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v.size += int64(n)
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}
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}
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// Flatten returns a flattened copy of this data.
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//
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// This method should not be used in any performance-sensitive paths. It may
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// allocate a fresh byte slice sufficiently large to contain all the data in
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// the buffer. This is principally for debugging.
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//
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// N.B. Tee data still belongs to this view, as if there is a single buffer
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// present, then it will be returned directly. This should be used for
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// temporary use only, and a reference to the given slice should not be held.
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func (v *View) Flatten() []byte {
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if buf := v.data.Front(); buf == nil {
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return nil // No data at all.
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} else if buf.Next() == nil {
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return buf.ReadSlice() // Only one buffer.
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}
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data := make([]byte, 0, v.size) // Need to flatten.
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for buf := v.data.Front(); buf != nil; buf = buf.Next() {
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// Copy to the allocated slice.
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data = append(data, buf.ReadSlice()...)
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}
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return data
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}
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// Size indicates the total amount of data available in this view.
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func (v *View) Size() int64 {
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return v.size
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}
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// Copy makes a strict copy of this view.
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func (v *View) Copy() (other View) {
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for buf := v.data.Front(); buf != nil; buf = buf.Next() {
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other.Append(buf.ReadSlice())
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}
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return
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}
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// Apply applies the given function across all valid data.
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func (v *View) Apply(fn func([]byte)) {
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for buf := v.data.Front(); buf != nil; buf = buf.Next() {
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fn(buf.ReadSlice())
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}
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}
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// Merge merges the provided View with this one.
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//
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// The other view will be appended to v, and other will be empty after this
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// operation completes.
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func (v *View) Merge(other *View) {
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// Copy over all buffers.
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for buf := other.data.Front(); buf != nil; buf = other.data.Front() {
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other.data.Remove(buf)
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v.data.PushBack(buf)
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}
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// Adjust sizes.
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v.size += other.size
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other.size = 0
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}
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// WriteFromReader writes to the buffer from an io.Reader.
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//
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// A minimum read size equal to unsafe.Sizeof(unintptr) is enforced,
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// provided that count is greater than or equal to unsafe.Sizeof(uintptr).
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func (v *View) WriteFromReader(r io.Reader, count int64) (int64, error) {
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var (
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done int64
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n int
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err error
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)
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for done < count {
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buf := v.data.Back()
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// Ensure we have an empty buffer.
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if buf == nil || buf.Full() {
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buf = bufferPool.Get().(*buffer)
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v.data.PushBack(buf)
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}
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// Is this less than the minimum batch?
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if buf.WriteSize() < minBatch && (count-done) >= int64(minBatch) {
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tmp := make([]byte, minBatch)
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n, err = r.Read(tmp)
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v.Append(tmp[:n])
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done += int64(n)
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if err != nil {
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break
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}
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continue
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}
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// Limit the read, if necessary.
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sz := buf.WriteSize()
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if left := count - done; int64(sz) > left {
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sz = int(left)
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}
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// Pass the relevant portion of the buffer.
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n, err = r.Read(buf.WriteSlice()[:sz])
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buf.WriteMove(n)
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done += int64(n)
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v.size += int64(n)
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if err == io.EOF {
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err = nil // Short write allowed.
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break
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} else if err != nil {
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break
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}
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}
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return done, err
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}
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// ReadToWriter reads from the buffer into an io.Writer.
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//
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// N.B. This does not consume the bytes read. TrimFront should
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// be called appropriately after this call in order to do so.
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//
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// A minimum write size equal to unsafe.Sizeof(unintptr) is enforced,
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// provided that count is greater than or equal to unsafe.Sizeof(uintptr).
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func (v *View) ReadToWriter(w io.Writer, count int64) (int64, error) {
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var (
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done int64
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n int
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err error
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)
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offset := 0 // Spill-over for batching.
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for buf := v.data.Front(); buf != nil && done < count; buf = buf.Next() {
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// Has this been consumed? Skip it.
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sz := buf.ReadSize()
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if sz <= offset {
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offset -= sz
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continue
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}
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sz -= offset
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// Is this less than the minimum batch?
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left := count - done
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if sz < minBatch && left >= int64(minBatch) && (v.size-done) >= int64(minBatch) {
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tmp := make([]byte, minBatch)
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n, err = v.ReadAt(tmp, done)
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w.Write(tmp[:n])
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done += int64(n)
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offset = n - sz // Reset below.
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if err != nil {
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break
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}
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continue
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}
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// Limit the write if necessary.
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if int64(sz) >= left {
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sz = int(left)
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}
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// Perform the actual write.
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n, err = w.Write(buf.ReadSlice()[offset : offset+sz])
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done += int64(n)
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if err != nil {
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break
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}
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// Reset spill-over.
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offset = 0
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}
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return done, err
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}
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